Vibratory screen systems have long been employed in both circular and rectangular form. The devices typically include a resiliently mounted housing having a screen extending across the housing. A vibration generating drive is coupled with the housing to vibrate the screen in an advantageous manner to increase screening efficiency. The screens are either self-contained by including screen cloth tensioned and bonded to a frame or rely on mechanisms on the resiliently mounted housing for placement and tensioning. In the latter circumstance, the screen typically includes screen cloth to which may be mounted hooks or eyes for attachment of tensioning mechanisms associated with the housing.
Alternatively, screens can include a perforated plate with screen cloth bonded thereto. When a plate is used, the screen may be tensioned before bonding to the plate. The screen cloth may be bonded to the plate by a layer of epoxy or thermoplastic material. The bonding material is positioned on the plate and the screen tensioned thereover. The material is then treated, commonly by heating to either initiate curing of the epoxy or fusing of the thermoplastic material. Nonstick layers of Teflon sheet may be employed where the assembly is compressed during the curing or fusing step. Multiple layers of screen cloth are known to be used in such assemblies.
Screens which employ hooks or eyes for tensioning by a separate mechanism have also been known which include laminated layers. A bonding by spot welding, epoxy or fusible material are known. Further, fusing multiple layers of screen cloth into the top of a frame structure made of fusible material having a peripheral frame and a pattern of open cells defined by cell walls has been done. The multiple screen cloths are bonded to the frame and to the cell walls by fusing the frame structure and resolidifying it after impregnation through the screen cloth or cloths. Such a structure is disclosed in U.S. Pat. No. 5,851,393, the disclosure of which is incorporated herein by reference.
Where bonding and laminating occurs in such a manner that the bonding or laminating material passes through the screen cloth or screen cloths to form a surface at the screening surface of the screen, a smooth surface results. The screen cloth often transports the material to be screened in a desired pattern. These smooth surfaces allow the material being screened to slip rather than transport the material and the overall transport of the material is inhibited.